Nowadays, it is known that activated porous carbon materials behave high specific capacitance owing to their high specific surface area, microporous and mesoporous structures. Therefore, the carbon materials with low cost and good cycle stability become one of the most promising electrode materials in supercapacitors. In this paper, the carbon material prepared by the carbonization of wild rice stem and the alkali activation possesses high specific surface area up to 1228 m(2)/g, which makes it more hopeful application prospects in electrochemical field. The results indicate that activation temperature and alkali concentration play important roles in improving the performance of specific capacitance of the activated carbon. The activated porous carbon prepared at 800 degrees C with a KOH/wild rice stem mass ratio of 3 shows the best performance and displays a specific capacitance of 301 F/g at current density of 1 A/g in a three-electrode configuration. Furthermore, the assembled symmetric supercapacitor attains a high energy density of 13.05 Wh/kg at the power density of 250 W/kg in 6 M KOH electrolyte. So the activated porous carbon made from wild rice stem is a low-cost, eco-friendly and high performance material for supercapacitors. (C) 2018 Published by Elsevier B.V.